What is welding slag inclusion?

Welding slag inclusions are generally divided into two categories.  The first type is metal slag, especially tungsten, copper and other metal particles residual in the weld, commonly known as tungsten, copper clip.The second type is non-metallic slag, especially refers to the residual slag in the weld after welding, including electrode coating or flux, sulfide, oxide and nitride, etc.According to its formation, can be divided into point slag, linear slag, chain slag and dense slag.

Slag inclusion will reduce the plasticity and toughness of the weld, and the slag inclusion with sharp Angle will produce stress concentration at the tip, and the tip will also develop as a crack source, especially in the weld with large air quenching tendency.Under the action of stress, cracks will first appear and spread along the slag in the welding seam, leading to the reduction of strength and weld cracking.

There are many factors to form welding slag inclusion. If there are more inclusions in welding materials (including base metal, gas and welding material, etc.), it is bound to cause inclusion in welding seam.  In addition, technological factors also have a great influence on welding slag inclusion.

1.Slag is not removed from the edge of the weldment, between the weld layer and the bead.  

Especially the use of alkaline electrode, if the slag is not removed, it is easier to produce slag;

2.Welding current is too small

melting metal and slag heat is insufficient, so that its fluidity is reduced, and molten metal solidification speed, slag too late to surface.

3.Improper chemical composition of base metal and welding material  

For example, when the molten pool contains more oxygen, nitrogen, sulfur and other components, its products (oxides, nitride, sulfide, etc.) in the case of faster solidification of molten metal, too late to emerge, will remain in the weld to form slag.